<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      #canvas {
        border: 1px solid;
      }
    </style>
  </head>

  <body>
    <canvas width="400" height="400" id="canvas"> 请升级你的服务器 </canvas>
    <script>
      var canvas = document.querySelector("#canvas");
      var context = canvas.getContext("2d");
      context.beginPath();
      context.moveTo(100, 100);
      context.lineTo(100, 200);
      context.lineWidth = 20; // 线的宽度
      //   context.lineCap='butt'; // 默认 线帽
      //   context.lineCap='round';
      context.lineCap = "square";
      context.strokeStyle = "#000";
      context.stroke();
    </script>
  </body>
</html>
